feat(config): add support for ES modules

- Add support for ES modules via `esModule` property in file config object

* test(modules): ensure relative paths work correctly

* test(e2e): module-types

`esModule: true` is now `type: 'module'`.  Test updated to reflect that.

static/context.html

@@ -26,7 +26,12 @@
   </script>
   <!-- Dynamically replaced with <script> tags -->
   %SCRIPTS%
-  <script type="text/javascript">
+  <!-- Since %SCRIPTS% might include modules, the `loaded()` call needs to be in a module too.
+   This ensures all the tests will have been declared before karma tries to run them. -->
+  <script type="module">
+    window.__karma__.loaded();
+  </script>
+  <script nomodule>
     window.__karma__.loaded();
   </script>
 </body>

static/debug.html

@@ -28,7 +28,12 @@
   </script>
   <!-- Dynamically replaced with <script> tags -->
   %SCRIPTS%
-  <script type="text/javascript">
+  <!-- Since %SCRIPTS% might include modules, the `loaded()` call needs to be in a module too.
+   This ensures all the tests will have been declared before karma tries to run them. -->
+  <script type="module">
+    window.__karma__.loaded();
+  </script>
+  <script nomodule>
     window.__karma__.loaded();
   </script>
 </body>

test/e2e/module-types.feature

@@ -0,0 +1,35 @@
+Feature: ES Modules
+  In order to use Karma
+  As a person who wants to write great tests
+  I want to use different script types with Karma.
+
+  Scenario: Globbing modules, with both .js and .mjs extensions
+    Given a configuration with:
+      """
+      files = [
+        { pattern: 'modules/**/*.js', type: 'module' },
+        { pattern: 'modules/**/*.mjs', type: 'module' },
+      ];
+      // Chrome fails on Travis, so we must use Firefox (which means we must
+      // manually enable modules).
+      customLaunchers = {
+        FirefoxWithModules: {
+          base: 'Firefox',
+          prefs: {
+            'dom.moduleScripts.enabled': true
+          }
+        }
+      };
+      browsers = ['FirefoxWithModules'];
+      frameworks = ['mocha', 'chai'];
+      plugins = [
+        'karma-mocha',
+        'karma-chai',
+        'karma-firefox-launcher'
+      ];
+      """
+    When I start Karma
+    Then it passes with like:
+      """
+      Executed 4 of 4 SUCCESS
+      """

test/e2e/support/modules/__tests__/minus.test.mjs

@@ -0,0 +1,11 @@
+import { minus } from '../minus.mjs'
+
+describe('minus', function () {
+  it('should pass', function () {
+    expect(true).to.be.true
+  })
+
+  it('should work', function () {
+    expect(minus(3, 2)).to.equal(1)
+  })
+})

test/e2e/support/modules/__tests__/plus.test.js

@@ -0,0 +1,11 @@
+import { plus } from '../plus.js'
+
+describe('plus', function () {
+  it('should pass', function () {
+    expect(true).to.be.true
+  })
+
+  it('should work', function () {
+    expect(plus(1, 2)).to.equal(3)
+  })
+})

test/e2e/support/modules/minus.mjs

@@ -0,0 +1,4 @@
+// Some code under test
+export function minus (a, b) {
+  return a - b
+}

test/e2e/support/modules/plus.js

@@ -0,0 +1,4 @@
+// Some code under test
+export function plus (a, b) {
+  return a + b
+}